Hitherto is known an inner rotor type motor in which a magnet is disposed on an inner peripheral side of a stator. In such an inner rotor type motor, as shown in a plan view in FIG. 14, a plurality of core pieces C1 are coupled by way of thin linking portions, so that a straight core C is formed. The straight core C is a member formed by blanking a flat plate made of magnetic material such a silicon steel plate, and a stator core stack U is formed by laminating a plurality thereof, as shown in a perspective view in FIG. 15. Each core piece has a core back Y and a tooth T. The stator core stack U has resin-made insulators, not shown, formed from both sides in the laminating direction (in the vertical direction in FIG. 15) of the straight cores C, and a winding P shown in FIG. 16 is wound on each tooth T in a straight state of the straight core C, as shown in FIG. 15.
After the winding P is wound on the tooth T, the linking portions of respective core piece C1 are folded and deformed in an annular form so as to join end surfaces X, X in the peripheral direction (see FIG. 15) of the stator core stack U, and thereby a stator S is formed. The stator S is fixed in a cylindrical housing H by such means as press-fitting and/or adhesive, as shown in a radial sectional view in FIG. 16.
At this time, an outer diameter of the stator S is formed slightly smaller than an inner diameter of the housing H, and an outer diameter size of the stator S has an influence on motor characteristics. That is, if an outer diameter size of the stator S is excessively smaller than an inner diameter size of the housing H, when the stator S is press-fitted into the housing H, a face pressure between an inner peripheral surface of the housing H and an outer peripheral surface of the stator S is becomes small, so that the stator S is not fixed firmly to the housing H. As a result coaxiality of the stator S and housing S deteriorates poor, and the stator S vibrates largely when the motor rotates.
To the contract, if an outer diameter size of the stator S is approximately equal to an inner diameter size of the housing H, when the stator S is press-fitted into the housing H, scoring forms in the housing H and/or the stator S at a contact area of the stator S and housing H, which leads to vibration of the stator S during motor rotation. In addition, if the stator S is press-fitted into the housing H, in such a scored state, the slot of the adjacent tooth T and tooth T in the peripheral direction of the stator S is uneven, and a magnetic field generated in the stator S by application of current is uneven in the peripheral direction, and the characteristic of the stator S deteriorates.
When the stator S is secured in the housing H by an adhesive, the stator S must be temporarily secured in the housing H by some means, until the adhesive is dried and moreover when an inflammable adhesive is used, a fireproof structure is newly required in the stator S and/or the housing H.